In a device for recording information onto an optical disk or reproducing information from an optical disk, when a single recording/reproducing laser beam is delivered onto a track in which information is to be recorded or has been recorded, two position-detecting laser beams that are symmetrical with respect to the recording/reproducing laser beam are also delivered onto the same track. These beams are generated by splitting a single laser beam from one light source (i.e. a laser) with a diffraction grating (for example, refer to Patent Document 1 and Non-Patent Document 1).
A single laser light source generally emits a single laser beam in a specific direction. Therefore, if multiple laser beams are required, it is necessary to use a diffraction grating or similar dispersing element to split one laser beam emitted from the light source, or provide two or more light sources.
Accordingly, if multiple laser beams can be generated from a single element, the diffraction grating will no longer be necessary, so that the device will be downsized and its production cost will be decreased.
On the other hand, it is known that a laser using a two-dimensional photonic crystal normally emits a single laser beam in a direction perpendicular to the two-dimensional photonic crystal (for example, refer to Patent Document 2) yet allows the emitting direction of the laser beam to be controlled by appropriately shaping the holes created in the two-dimensional photonic crystal (refer to Non-Patent Document 2). This is because an appropriately shaped hole improves the light-confining property (which is represented by a Q// value) with respect to the direction parallel to the two-dimensional photonic crystal in a photonic band in which the group velocity becomes zero when the component k// of the wave number vector parallel to the two-dimensional photonic crystal is at a non-Γ point, i.e. when k// is not zero.
However, Non-Patent Document 2 makes no mention as to the number of laser beams emitted from the laser and thereby offers little help in the development of a device that requires multiple laser beams (e.g. the aforementioned optical disk recording/reproducing device).    Patent Document 1: U.S. Pat. No. 3,876,842    Patent Document 2: Japanese Unexamined Patent Application Publication No. 2000-332351    Non-Patent Document 1: Ryoichi Ito and Michiharu Nakamura, Handoutai Rehza [Kiso To Ouyou] (Semiconductor Laser [Basics and Applications]), pp. 305-306, published Apr. 25, 1989, Baifukan Co., Ltd, Tokyo    Non-Patent Document 2: Eiji Miyai et al., “Fotonikku Kesshou Men Hakkou Rehza No Gamma-Ten Igai Deno Hasshin No Kanousei No Kentou (Study on the Possibility of the Oscillation of a Photonic Crystal Surface Emitting Laser at a Point other than the Γ Point)”, Preprints of 67th Meeting of Japan Society of Applied Physics (Issued Aug. 29, 2006), Part 3, p. 968, Japan Society of Applied Physics